The invention relates to a direct-acting, pressure-balanced and servo-controlled solenoid valve for directing fluids.
A direct-acting, pressure-balanced valve of this nature is known from EP 0 681 128 A1. This valve consists of a housing with at least two connections, as well as of a solenoid and a core which is slideably guided within a hollow cylinder in the solenoid body, and is connected to the valve body. A valve seat is assigned to this valve body. The core has oppositely arranged end faces and a central bore which establishes the connection between the active spaces. The core is here provided with a seal in order to divide two connection spaces, the outer diameter of the seal corresponding to the diameter of the valve seat. This measure ensures that the valve is pressure-balanced. The core, pressure-balanced in this way and containing the seat seal, is pressed by the force of a closing spring onto the valve seat which is rigidly connected to the valve body.
It has been found to be a disadvantage of the valve type mentioned that the main valve seat is formed at the valve housing, and the elastic seat seal is on the mobile side of the core, the membrane or the piston. This means that for a pressure-relieved design it becomes necessary to match the surfaces carefully with respect to each other which, depending on manufacturing tolerances, is never 100% possible.
Also known are servo-controlled valves of the above-mentioned type in which, initiated by the actuation of a magnet, opening and closing forces are generated by means of differential pressure surfaces and the operating medium. To this purpose the valve body is connected to the core by way of a connecting piece. As soon as the solenoid excites the core, only the core is moved in the first movement phase. In the second part of the movement process, the core entrains the connecting piece together with the valve body, and opens the valve. In the case of servo-controlled valves, this second phase is generally assisted by the pressure of the medium which is allowed to flow through a choke bore in the membrane or in the piston into the opposite active space above the piston, thereby assisting the magnetic forces.
When the pilot valve is closed, the pressure above the piston builds up via the choke bore. The main valve is closed by the pressure of the medium assisted by the force of the closing springs, on account of the larger effective surface above the piston. When the pilot valve opens, a relief bore becomes free, which leads to a pressure reduction in the active space above the piston. Because of the coupling between the solenoid core and the piston, the latter also moves upwards during the upward movement.
It has been found to be of particular disadvantage with these servo-controlled valves that there is the danger of the choke bore becoming blocked by dirt particles, or for example in the case of water valves there is the risk of this bore becoming obstructed by deposits of lime scale. This means that the function of the valve is nullified and, furthermore, the application possibilities of these valves become limited to a few, preferably filtered media.
The invention provides a cost-effective, durable and energy-saving valve which combines the advantages of direct-acting valvesxe2x80x94reliable closing function at zero pressure and fast opening of the valvexe2x80x94with the advantages of the servo controlxe2x80x94switching of high pressures with small magnetic forces and reliable closing.
In the solenoid valve according to the invention, the entire available magnetic force is used exclusively for the opening process. To this purpose a differential pressure surface equal to zero is produced. By this measure, a medium-assisted, reliable and intensified closing is forced after the solenoid is switched off.
Furthermore it is provided that the dirt-sensitive choke bore, generally used in servo-controlled valves, is produced by open channels, which bore is defined by the lip of a robust and temperature-insensitive groove and lip seal in the form of closed rectangles, the lip surrounding the core. This solution achieves to advantage that the to-and-from movement of the core cleans the lip of the groove and lip seal from deposit-forming contamination, such as vapor, and so ensures that the functionality of the valve is not impaired by deposits forming at the groove and lip seal and in the open channel, respectively.
The valves functioning in this way, which may be produced as straight-seat as well as slanted seat valves, may be used universally for directing neutral media, such as water and gases, the temperature range being limited only by the durability of the groove and lip seal. Furthermore, these valves, when made of different materials, for example plastics such as PVC, PVDF, PEEK, can also be used for aggressive media or in analytical and medical applications.
By virtue of the proposed arrangement, complete differential pressure relief in the seat valve is achieved in that the elastic main seat seal is preferably fitted inside the housing, and the seat and balance diameters are arranged by combination in the mobile seat bushing.
In a further advantageous embodiment as a slanted seat valve, a fixed cartridge with a main seat seal is fitted inside the housing. Here, too, the seat and balance diameters are arranged by combination in the mobile seat tube.
The valves provided by the invention may be embodied as 2/2xe2x80x94 as well as 3/2xe2x80x94port directional control valves. The design of the valves is distinguished in that it renders possible a simple production and assembly, whereby the manufacturing costs are reduced. Furthermore, the user is provided with an almost maintenance-free valve of long life.